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Oceanographic Survey

OCEANOGRAPHIC SURVEY

OCEANOGRAPHIC SURVEY. Surveys are conducted by the U.S. Navy and civilian government agencies. By their nature, surveys are systematic examinations of the oceans' condition. Although the methods used to conduct these studies have evolved over the last two centuries, expressions such as "sailing in uncharted waters" and "seizing the weather gauge" still attest to their importance.

Early Surveys

All mariners know that accurate information about winds, tides, currents, and ocean bottom depth raise the likelihood of a safe passage. In naval terms, superior "environmental intelligence" can allow one side to gain advantage over the other. In the nation's early years, this knowledge was held by individual seafarers and naval officers, or published, with varying degrees of accuracy, by foreign countries and private commercial operations. In 1807, Congress authorized the creation of a Survey of the Coast to obtain and map basic information about the nation's islands, shoals, and anchorages. The U.S. Navy established the Depot of Charts and Instruments in 1830 to supply accurate nautical charts, books, and navigational instruments to the Navy and American shipping interests. The navy published its first charts in 1837, four maps of the fishing banks off the coast of Massachusetts.

In the 1840s, the practice of oceanographic surveying took a significant step forward on both the naval and civilian sides. Recognizing the need to keep all hydro-graphic (pertaining to nautical surveys and charts) materials in one place, in 1842 Congress authorized building a central repository for the Depot's collections. The Depot's superintendent, navy officer Matthew Fontaine Maury, made several key advances in the science of hydrography. First, he and his staff reviewed all of the hundreds of ships' logs in their care. By systematically comparing conditions for the same location in different seasons, Maury could suggest navigational routes that maximized speed and safety. The resulting Wind and Current Charts were soon the reference of choice worldwide. Maury also created a template for a standardized log that all navy captains were required to complete for every voyage and to submit to the Depot. Merchant and foreign vessels received copies of Wind and Current Charts as well in exchange for keeping Maury's logs. Within five years the Depot had received 26 million reports.

Meanwhile, Alexander Dallas Bache took the helm of the U.S. Coast Survey in 1843. Bache raised the level of scientific inquiry in the name of more accurate charts and navigation. His study of the gulf stream, begun in 1845, sought new measures to determine the dynamics of what he suspected was an ever-changing current. For more than a decade, survey ships repeatedly measured temperature at the surface and varying depths, described the bottom depth and character, recorded direction and speed of the currents and the surface and at varying depths, and examined plant and animal life along the way.

Technological Advances

Maury and Bache had laid the groundwork for American scientific exploration of the ocean. Their principle of repeated, systematic observation remains the guiding philosophy; only the tools have changed. In some instances, surveys have supported the deployment of new technologies. For example, entrepreneurs who wanted to set up a telegraph connection across the Atlantic required information about the ocean floor. The resulting survey produced the first published depth chart of the Atlantic Ocean, and in 1858 the first telegraphic messages were sent across the ocean via cable lying on the seabed.

New missions sometimes required new technologies. In the 1870s, Coast Survey officer Charles Sigsbee modified a prototype invented by Sir William Thomson (later Lord Kelvin) to construct a machine that used wire instead of rope to take depth soundings. Sigsbee's sounding machine was used to produce a bathymetric (deep-water depth) chart of the Gulf of Mexico in 1874–1875, the first modern and accurate map of any portion of the deep ocean. Sigsbee and biologist Alexander Agassiz collaborated to replace the rope used to raise and lower equipment with lines made of steel wire. Following this idea, Coast Survey officers developed steel wire lines that allowed vessels to anchor at abyssal depths.

By the 1870s, fish and shellfish stocks showed signs of decline and disputes arose among fishermen over the fairness of some of the new netting and dredging techniques. The Coast Survey worked with the newly created U.S. Fish Commission (1871) to conduct dredging operations of their own to survey fish populations. Coast Survey and Fisheries Commission ships discovered hundreds of marine species on their biological research expeditions crossing the world. In 1878, the Coast Survey merged with the Geodetic (size and shape of the earth) Survey to become the U.S. Coast and Geodetic Survey (C&GS), which began to produce the most complete and accurate maps yet of the United States.

During the last quarter of the nineteenth century, Navy oceanographers turned their attention to Central America, where they assisted in locating suitable sites for a canal linking the Gulf of Mexico and the Pacific Ocean, sparing ships the long and dangerous trip around the tip of South America. Nor had the government given up the idea of a Northwest Passage—a route linking the Atlantic and Pacific via the Arctic Sea. Several expeditions were sent to explore the ice; navy civil engineer Robert Peary reached the North Pole in 1909. The disastrous sinking of the Titanic in 1912 also focused new attention on monitoring ice from the polar sea.

During World War I (1914–1918), German submarines posed a new and frightening threat, sinking forty-five U.S. ships while cruising in American waters. American researchers pursued the idea of underwater listening devices as a way to track the U-boats, although the first workable system was not built until after the war. Sonar, the use of sound echoes to locate underwater features and submerged objects, revealed the sea bottom's topography in much greater detail than possible before. In the 1920s, C&GS vessels began to use echo-sounding equipment alongside the traditional wire line to determine accurate values for the velocity of sound in seawater. Survey ships mapped the terrain of the continental shelf, information that would prove valuable for hunting German submarines during World War II (1939–1945). On the eve of World War II, the navy explored the effects of water temperature and salinity on sound transmission underwater, further refining its ability to locate underwater targets.

World War II, and the renewed threat of submarine warfare, spurred more innovative firsts, including deep-sea cameras and electronic navigation systems that used reflected radio waves (radar). Intended originally as a tool in precision aerial bombing, radar was being used by the C&GS to conduct hydrographic surveys by the war's end. Demand for accurate charts had skyrocketed in the wake of Pearl Harbor. The navy's Hydrographic Office dispatched survey ships with onboard printing equipment to accompany the Pacific fleet—43 million charts were printed and issued in one year.

The decades after World War II were notable for collaboration between civilian government agencies, the C&GS, the navy, and academic institutions. One landmark expedition took place in 1955, when the C&GS ship Pioneer was engaged by the navy to survey the West Coast out to several hundred miles offshore. The Scripps Institute of Oceanography attached a newly designed tow to the Pioneer that would measure magnetic properties of the seabed. The project mapped previously unknown long, magnetic stripes that lay along the ocean floor. This discovery, along with the identification of the Mid-Atlantic Ridge Rift Valley in 1959, and C&GS scientists' studies of underwater earthquakes, ultimately led Princeton University professor Harry H. Hess to outline a theory of plate tectonics in the early 1960s.

The 1960s were a time of rapid advancement in oceanographic surveys. The C&GS built a fleet of new survey ships and spent more than a decade mapping large areas of the North Pacific basin for the Seamap Project. New technical advances included the Deep Tow instrument system, which takes multiple measures of the deep sea environment; multibeam sounding systems, which can take simultaneous readings of a swath of ocean floor to generate a map almost instantly; and the submersible re-search vessel Alvin, which can take scientists to unprecedented ocean depths. Research also focused on the inter-action between ocean and atmosphere, which was reflected in the creation of the National Oceanic and Atmospheric Administration (1970) that now encompasses the C&GS as well as the National Weather Service.

Technological advances of the late twentieth century included satellite communication and observation, global positioning, microchip technology, computers small enough to be taken into the field, and more sophisticated modeling techniques. One widely used practical application is the navy's Optimum Track Ship Routing program that uses meteorological and oceanographic data to create a near-real-time forecast of the safest and most efficient passage across the seas. Future surveys are likely to take advantage of microchip technology and satellite communication to obtain large-scale, real-time maps that use remote sensors to transmit data from a vast expanse of ocean. For instance, passive acoustic monitors positioned in the water all over the globe already have been used to detect deep-sea volcanic eruptions and the migratory paths of the blue whale. These technologies, along with even greater computer processing capability, may take oceanographers ever closer to obtaining a pulse of the planet.

BIBLIOGRAPHY

Charts from the U.S. Coast Survey. Available from http://chartmaker.ncd.noaa.gov.

Labaree, Benjamin W., et al. America and the Sea: A Maritime History. Mystic, Conn.: Mystic Seaport Museum, 1998.

National Oceanic and Atmospheric Administration. Home page at http://oceanexplorer.noaa.gov.

Naval Oceanographic Office Home page at http://www.navo.navy.mil.

Pinsel, Marc I. 150 Years of Service on the Seas: A Pictorial History of the U.S. Naval Oceanographic Office from 1830 to 1980. Washington, D.C.: Department of the Navy, Oceanographic Office, 1982.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration. Discovering Earth's Final Frontier: A U.S. Strategy for Ocean Exploration, The Report of the President's Panel on Ocean Exploration. Washington, D.C.: October 2000.

JenniferMaier

See alsoNavy, United States ; Titanic, Sinking of the .

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Oceanography

OCEANOGRAPHY

OCEANOGRAPHY. Although oceanography is a twentieth-century scientific discipline forged from European roots, several American developments in the nineteenth century contributed to its modern formation. First, federal interests in mapping the coastlines, charting seaports, and exploring the vast expanse of the United States inspired the work of the U.S. Coast Survey and the Navy's Depot of Charts and Instruments and the U.S. Exploring Expedition (1838–1842). Second, American educational reformers and intellectuals, with their gaze firmly set upon Europe, embarked on an overhaul of the American university system, adding comprehensive curricula in the sciences to colleges and universities for the first time.

In the nineteenth century, concerns had been voiced about the valuable European North Sea fishery and the cod fishery in New England leading to a new federal agency to investigate this resource. The U.S. Fish Commission gained support in 1871,and centered its activities in a laboratory at Woods Hole (Cape Cod) and on two ships dedicated for open-ocean fisheries work. Thus, when an international meeting was held in 1888 at Plymouth, England, to investigate the collapse of the North Sea fishery and when the International Council for the Exploration of the Sea (ICES) was formed in 1902, American scientists were prepared to participate.

Federal support for oceanography at this time was limited. Indeed, when Alexander Agassiz explored the Pacific and Atlantic at the end of the nineteenth century, he did so aboard Coast Survey and Fish Commission vessels but financed the work with his own personal resources. Thus, by the beginning of the twentieth century, Americans lagged behind the British, Germans, and Scandinavians.

American interests in the sea changed, however, first with the sinking of the Titanic (1912), and then from the American experiences in World War I (1914–1918). Both disasters illustrated the need to better understand the oceanic conditions in the North Atlantic and to develop underwater listening devices to protect the country from the new submarine warfare. Lacking a permanent scientific advisory group, President Woodrow Wilson transferred the wartime National Research Council (NRC) to the National Academy of Sciences (NAS) following the war. Continuing its work after 1919, the NRC sponsored re-search that led in the 1920s to the development and refinement of the sonic depth finder and sonar, acoustical devices that greatly improved navigation and enabled surface ships to detect submarines. With its newfound interest in the sea, the NAS established its Committee on Oceanography in 1927, charged with recommending federal oceanic policy.

By the early twentieth century, Americans already established a research presence alongside the ocean, at marine laboratories on both coastlines. The Marine Biological Laboratory (MBL) enhanced the research objectives of the Fish Commission laboratory at Woods Hole. On the West Coast, William Emerson Ritter established the Scripps Institution of Biological Research in La Jolla (near San Diego) in 1903. But neither Woods Hole nor Scripps had an extensive oceanic research program; indeed, American oceanography was barely in its infancy.

In 1924, Thomas Wayland Vaughan, a geologist, was appointed to direct the Scripps Institution of Oceanography (SIO). Three years later, he was named a member of the NAS's oceanographic committee. By the end of 1927, the committee began to support Vaughan's notion that the country needed "oceanographic stations" scattered along the American Pacific and Atlantic coastlines. Then in 1930, the Rockefeller Foundation announced the establishment of three oceanography centers, Scripps Institution in La Jolla, the Oceanographic Laboratories at the University of Washington, and a large new research center at Woods Hole, Woods Hole Oceanographic Institution (WHOI). Thus, by 1930, the institutional framework for the development of American oceanography was set.

The new scientific field developed rapidly, especially with the infusion of research money from philanthropic, federal, and military sources. The U.S. Navy encouraged developments in marine acoustics and related aspects of physical oceanography as it attempted to develop more sophisticated means to monitor the subsurface environment and to build deterrent devices for submarine warfare. This work led to more sophisticated sonar devices and the invention of hydrophones for submarine sound detection. Geological oceanography received attention especially as it offered a means to direct exploration of shallow oceanic basins for oil. Meteorological research continued at most oceanographic laboratories, attempting to understand the relationship between oceanic currents, open ocean wind patterns, and continental weather.

With the outbreak of World War II (1939–1945), oceanography's centrality to the American war effort was demonstrated once again. Of course, much attention focused on the development of submarine warfare. While at the outset of the war, the Allies lost an inordinate number of vessels, wartime matériel, and manpower to the German submarines, oceanographic developments led to dramatic improvements in submarine detection and, ultimately, to the production of submarines and submarine warfare that exacted an even greater toll from the Germans and Japanese. Not surprisingly, therefore, when the war ended in 1945, the federal government established the Office of Naval Research (ONR), which served to ensure funding for oceanographic centers throughout the United States. In addition, the presence of surplus Navy vessels created a surfeit of oceanic research platforms for American oceanographers.

Following the war, the emergence of the Cold War maintained the U.S. Navy patronage for oceanographic research. In addition to its traditional concerns, the Navy became interested in studying the deep ocean basins. This interest involved an extensive hydrophone system, connected by submarine cables to monitor the movement of Soviet submarines, so the deep basins in the Atlantic and Pacific posed potential problems. These same regions attracted increasing attention from oceanographers in the 1950s and 1960s as ideas of seafloor spreading and continental drift began to be discussed again. The existence of mid-ocean ridges and deep-sea trenches gave these notions added credence, but oceanographers needed new technological tools to investigate the bottom of the sea to validate the mechanism for any movement.

Water sampling, temperature measurements, and bottom sediments were soon the target of many research expeditions. Increasingly, this type of research became more expensive, multidisciplinary, and technological, requiring greater financial resources, larger groups of collaborating researchers, and, in many cases, international cooperation from oceanographic experts scattered worldwide.

With multiple partners, oceanography entered its current phase. Continuing to pursue deep ocean research, oceanographers worked to develop a new technological device, the deep-sea submersible. Following dramatic explorations of the earth's deepest marine trenches in the Trieste, American oceanographers argued for the creation of a highly maneuverable submersible that could withstand the demanding conditions of the oceanic depth. The Navy, too, was interested; after all, the hydrophone network it planned would need to be maintained. Then, the loss of the attack submarine Thresher in 1963 under-scored the Navy's interests. Working closely with engineers at Woods Hole and other oceanographers with sub-marine experience, the Alvin was commission in 1964 and the era of submersible research in oceanography entered its most dramatic phase.

By the 1970s, the Navy modified submersibles for its own purposes and Alvin and its successors were pressed into basic oceanographic research. In the late 1970s, oceanographers soon discovered sea vents adjacent to oceanic ridges worldwide. Even more dramatic, however, were the faunal forms inhabiting these vents. For the first time, luxuriant "gardens" of deep-sea animals, all new to science, were described. Plate tectonics was not just con-firmed, but the physical, chemical, and biological aspects of the vents opened a new era for oceanographic research. By the close of the century, new ideas concerning the origin of life, conditions for the emergence of life, sources for the chemical composition of seawater, and deep ocean sources for thermal conductivity created fresh perspectives for oceanographic work. Coupled with exciting extensions of the century-long work to study open-ocean currents, including work on the longitudinal oscillations of large masses of warm and cold water in the central gyres of the oceans that seem to affect the earth's climate, oceanography at the beginning of the twenty-first century promised to maintain its prominent role in scientific research.

BIBLIOGRAPHY

Benson, Keith R., and Philip F. Rehbock, eds. Oceanographic History: The Pacific and Beyond. Seattle: University of Washington Press, 2002.

Mills, Eric. Biological Oceanography, An Early History, 1870–1960. Ithaca, N.Y.: Cornell University Press, 1989.

Oreskes, Naomi, ed. Plate Tectonics: An Insider's History of the Modern Theory of the Earth. Boulder, Colo.: Westview Press, 2001.

Keith R.Benson

See alsoLaboratories ; Marine Biology ; Meteorology ; National Academy of Sciences ; Submarines .

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Oceanography

Oceanography

Oceanography, the study of the oceans , is a combination of the sciences of biology, chemistry, geology, physics , and meteorology .

Ancient explorers of the ocean were sailors and fishermen who learned about marine biology by observing the sea life and discovering when it was most plentiful. They observed the effects of wind , currents, and tides , and learned how to use them to their advantage or to avoid them. These early humans discovered that salt could be retrieved from seaweed and grasses.

Polynesians combined what they knew about the weather , winds, and currents to investigate the Pacific Ocean, while the Phoenicians, Greeks, and Arabs explored the Mediterranean Sea. The early Greeks in general and Herodotus (484428 b.c.) in particular believed that the world was round. Herodotus performed studies of the Mediterranean, which helped sailors of his time. He was able to take depth measurements of the sea floor by using the fathom as a unit of measure, which was the length of a man's outstretched arms. Today the fathom has been standardized to measure 6 ft (1.8 m) in length.

Aristotle (384322 b.c.) also studied marine life. One of his contemporaries, a geographer by the name of Poseidarius, studied the tides and their relationship to the phases of the Moon .

Pliny the Elder a.d.2379) was a Roman naturalist who discovered, by studying marine biology, that some organisms had medicinal uses. One of his predecessors, Seneca (4 b.c.a.d.65) predicted that interest in the oceans would fade and "a huge land would be revealed," foreshadowing the age of exploration and discovery of the New World. A period of about 1,000 years followed when no new studies were done until the fifteenth century. Christopher Columbus performed oceanographic studies on his voyages.

Captain James Cook , the explorer, was one of the first scientists to study the oceans' natural history. A surge in scientific studies took place in the seventeenth century, during which scientists tried for the first time to combine the scientific method with sailors' knowledge.

U.S. Navy lieutenant Matthew Fontaine Maury (18061873) is considered the father of modern oceanography. It was during the nineteenth century that the name was given to the science.

In December 1872, the British ship HMS Challenger began a four-year journey, which lasted until May of 1876. This was the first major study of the ocean approached from a scientific viewpoint, and since that time significant strides have been made. The advent of submersible vehicles allowed for first-hand study of the ocean floor and the water above it. In 1900, Prince Albert of Monaco established two institutes to study oceanography.

Two areas of focus within oceanography today are physical and chemical oceanography. Physical oceanography is the study of ocean basin structures, water and sediment transportation, and the interplay between ocean water, air and sediments and how this relationship affects processes such as tides, upwellings, temperature , and salinity. Findings aid oceanic engineers, coastal planners, and military defense strategists. Current areas of research also include oceanic circulation, especially ocean currents and their role in predicting weather-related events, and changes in sea level and climate.

Chemical oceanography investigates the chemical make-up of the oceans. Many studies in this area are geared to understanding how to use the oceans' resources to produce food for a growing population.

Even though the study of the oceans has entered the technological age, there is much still unexplored and unknown. Oceanographers of the 1990s use satellites to study changes in salt levels, temperature, currents, biological events, and transportation of sediments. Deep-sea studies are underway using unmanned robotic submersible craft to study ocean floor hydrothermal vents, sea-floor spreading , and subduction zones that lie beneath the ocean floor. As scientists develop new technologies, the future will open new doors to the study of oceanography.

See also Bathymetric mapping; Beach and shoreline dynamics; Continental drift theory; Continental shelf; Convergent plate boundary; Coral reefs and corals; Delta; Depositional environments; Desalination; Douglas sea scale; Dunes; Earth (planet); Earth science; Earth, interior structure; El Nino and La Nina phenomena; Geothermal deep ocean vents; Global warming; Gulf of Mexico; Gulf stream; Guyots and atolls; Hawaiian Island formation; History of exploration II (Age of exploration); Hydrogeology; Hydrologic cycle; Hydrothermal processes; Icebergs; Land and sea breeze; Latitude and longitude; Marine transgression and marine regression; Mid-ocean ridges and rifts; Ocean circulation and currents; Ocean trenches; Oceans and seas; Offshore bars; Petroleum; RADAR and SONAR; Red tide; Saltwater encroachment; Seawalls and beach erosion; Tides; Wave motions

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Oceanography from Space

Oceanography from Space

The use of space satellite data for ocea n observations allows marine scientists to view biological, chemical, and physical interactions within the oceans on regional and global scales. Satellite studies have revolutionized our ideas of how the ocean works. Satellite sensors measure a myriad of different phenomena including: sea surface temperature, surface wind, ocean color and productivity, ocean height, tides, and currents.

Altimeter Data

Several different in struments are used to collect oceanographic measurements. For example, the TOPEX/Poseidon satellite measures the height of the sea surface using an altimeter . The altimeter flies aboard the satellite at approximately 1,335 kilometers (830 miles) above Earth and emits a radar pulse that reflects off the sea surface. Because the speed of the pulse and location of the satellite are known, scientists can calculate the height of the sea surface.

In addition, the strength of the radar signal depends on the size of the surface ripples, which are in turn related to the wind speed, allowing the wind speed to be calculated. Because currents are detectable as slopes in the sea surface, the world's ocean currents can also be identified and monitored.

Altimeter data is also used for identifying the topography of the seafloor. For example, when there is a topographic high, such as a mountain on the seafloor, then there is a related topographic high or "mountain" in the sea level. This seafloor feature can be a subsurface seamount , or it may be a local increase in density in the Earth's crust.

Radiometer Data

A radiometer can be used to collect surface temperature data and ocean color data. A radiometer measures the amount of the Sun's visible light and infrared radiation reflected off the ocean. Examples of radiometers include the Coastal Zone Color Scanner (CZCS) and SeaWiFS (Sea-viewing Wide Field-of-view Sensor).

The temperature of the sea surface can be calculated using the infrared portion of the data. Because currents and water masses vary considerably in temperature, this data is particularly useful in observing currents and circulation processes.

Eddies are one feature in particular that can be identified using an infrared radiometer. These are generated by large-scale currents, such as the Gulf Stream. Eddies can affect the distribution of marine life and can last for many years before dissipating. Locating such eddies and studying their dynamics can help researchers track pollution such as oil spills and determine where marine life may be located.

Ocean Color.

Ocean color can be determined by measuring the portions of the visible spectrum reflected from the ocean surface. It can indicate a number of things to an oceanographer, such as amount of plankton and amount of vegetation. The color of the ocean changes slightly, from a bright blue to a dark blue or black when plankton float freely or concentrate in areas. These concentrations are called blooms. These colors can indicate to scientists the productivity of the oceans and potential for greater amounts of wildlife since plankton are the basis of the marine food web and without plankton all marine life would suffer.

Satellite data have become accurate and dependable enough that they is now integrated with other forms of marine data collection. In addition, satellite data provide a large-scale view of ocean dynamics that otherwise would be unavailable. What has emerged is exciting new information about vast areas of previously unstudied open water.

see also Algal Blooms in the Ocean; Ocean Currents; Ocean-Floor Bathymetry; Ocean Mixing; Weather and the Ocean.

Alison Cridland Schutt

Bibliography

Mellor, George L. Introduction to Physical Oceanography. New York: Springer Verlag, 1996.

Ross, David A. Introduction to Oceanography, 5th ed. New York: HarperCollins College Publishers, 1995.

Sandwell, David T. "Geophysical Applications of Satellite Altimetry." Reviews of Geophysics. supplement (1990):132-137.

SATELLITE PHOTOGRAPHS

This encyclopedia contains several photographs taken from satellites. Entries with notable images include:

  • "Algal Blooms in the Ocean"
  • "Bays, Gulfs, and Straits"
  • "Geospatial Technologies"
  • "Marginal Seas"
  • "Microbes in the Ocean"
  • "Ocean Mixing"
  • "Ocean-Floor Sediments"

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Mid-Ocean Ridges and Rifts

Mid-ocean ridges and rifts

The ocean floor is mountainous and uneven, much like Earth's surface. As oceanographers began mapping the ocean bottom, they discovered that the sea floor is full of vast rising slopes, or ridges, and dramatic open valleys, or rifts. During World War II, oceanographer William Maurice Ewing began mapping the complex ocean bottom with sophisticated instruments such as sonar depth finders and underwater cameras that helped trace the contours of the ocean bottom. Ewing set out to measure and record a massive chain of undersea mountains called the Midatlantic Ridge. When Ewing and his crew began mapping the massive ridge, they encountered a problem: the sonar beams were bouncing back. This problem led to another great discovery. They realized that there were frequent oceanic earthquakes occurring along the ridge. This was an exciting discovery because it opened up the possibility that oceanic earthquakes might be connected to ridges and rifts. Using data from other expeditions, Bruce Charles Heezen (b. 1924) more accurately measured the Midatlantic Ridge as he began mapping the ocean floor. The Ridge measured up to 1.9 miles (3 km) high and 45,954 miles (73,940 km) long. Interestingly, however, he detected a gully in the ridge that led to the Heezen-Ewing theory in 1958, which formally recognized the Midatlantic Ridge as containing a rift. Their discovery sparked interest in other scientists and explorers who questioned the existence of other rifts in ocean ridges.

In the late 1950s, American and Soviet oceanographic vessels began mapping the ocean floor so that their nuclear submarines could navigate deep underwater. The ensuing data provided maps that revealed extraordinary natural phenomena. Submerged peaks and undersea ridges form a continuous mountain chain that reaches up to 10,000 feet (3,048 m) and measures 40,000 miles (64,360 km). This mid-ocean ridge system circles the earth several times and is now known as one of Earth's dominant features, extending over an area greater than all the major land mountain ranges combined. Along a great deal of its length, the ridge system is sliced down its middle by a sharp gully, a rift that is the outlet of powerful heat flows. Temperature surveys demonstrate that heat seeps out of the earth in these mountainous regions of the middle Atlantic, adding to the complexity of the ocean floor. This evidence of heat emitting from Earth's giant cracks and faults helped reveal the existence of earthquakes and volcanic eruptions beneath the ocean. Most of this heat and movement take place in the Atlantic Ocean where the ridge is steeper and more jagged than in the Pacific or Indian Oceans .

In some of the most active volcanic areas another unusual natural phenomenon takes place, discovered by Harry Hammond Hess . Hess studied the isolated mountains rising from the ocean floor and discovered "sea-mounts," which he named guyots in honor of the Swiss-American geographer Arnold Henry Guyot (18071884). Hundreds of these strange undersea protrusions lie under the Pacific Ocean, all of which were probably sunken islands created from volcanic lava . Some of these guyots broke away and gradually wandered further away from the volcanoes. Before oceanographers studied the floor of the great oceans, there was little evidence to support the continental drift theory , which assumed that all the great landmasses were once joined in one supercontinent. Hess's discovery of guyots and other studies of seafloor movement helped reveal the spreading movement of the ocean floor. Hess proposed that hot rock swelled from deep within the earth, constantly forcing the ridges and rifts to part and spread. Later these discoveries of seabed movement helped build on the findings of Alfred L. Wegener's thoery of continental drift.

See also Sea-floor spreading

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oceanography

oceanography, study of the seas and oceans. The major divisions of oceanography include the geological study of the ocean floor (see plate tectonics) and features; physical oceanography, which is concerned with the physical attributes of the ocean water, such as currents and temperature; chemical oceanography, which focuses on the chemistry of ocean waters; marine biology, the study of the oceanic flora and fauna; and, in meteorology, the interaction between the atmosphere and the ocean.

Oceanography as a comprehensive study dates from the Challenger expedition (1872–76), directed by the naturalists C. W. Thomson, a Scot, and John Murray, a Canadian. The term oceanography became current through reports of the expedition edited by Murray, who later became a leader in the study of ocean sediment. The success of the Challenger expedition and the importance of ocean knowledge to shipping, fisheries, the laying of telegraph cables, and climatological studies led many nations to send out expeditions.

Universities and private individuals, as well as governments, have established institutions for the study of the ocean; there exist today about 250 such institutions. One of the earliest was the marine biological station at Naples (founded 1872), which stimulated the founding of many other seaside stations, some of which, e.g., the Scripps Institution of Oceanography at La Jolla, Calif., have enlarged their activities to include all fields of oceanographic research. Other notable institutions in the field include the Oceanographic Museum at Monaco (1910); the biological station of the Univ. of Oslo; the Woods Hole Oceanographic Institution at Woods Hole, Mass. (1930); and the Lamont-Doherty Geological Observatory of Columbia Univ (1949).

The first international oceanographic organization was the International Council for the Exploration of the Sea (1901). In 1966 the U.S. Congress created the National Council for Marine Resources and Engineering Development charged with exploring all aspects of ocean development, and authorized the National Science Foundation to sponsor sea-grant colleges analogous to the Dept. of Agriculture's sponsorship of land-grant colleges. Projects such as Conshelf, under Jacques Cousteau; Sealab, under the U.S. Navy; Tektite, a cooperative venture of the U.S. Dept. of the Interior and the National Aeronautics and Space Administration; Aquarius under the National Oceanic and Atmospheric Administration; and others have established temporary stations in oceans to see whether humans can live and work underwater for extended periods.

Modern deep-diving equipment has been improved to permit descents to very great depths, such as the U.S. bathyscaphe, Trieste II, which descended to 35,798 ft (10,294 m) in the Marianas Trench in 1960. Smaller, remote-controlled craft, such as the Jason, which was used to examine the sunken steamship Titanic, explore natural and humanmade underwater structures. Deep-diving craft (see submersible) provide invaluable direct observations of the deep ocean bottom, mid-ocean ridges, and marine life. Recent oceanographic studies include drilling of the seafloor (see Deep Sea Drilling Project).

See M. G. Gross, Oceanography: A View of the Earth (1972); R. R. Ward, Into the Ocean World (1974); M. G. Gross, Oceanography (1990); R. A. Davis, Oceanography: An Introduction to the Marine Environment (1987, 2d ed. 1991); J. Cone, Fire Under the Sea (1992).

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Oceanography

Oceanography

Oceanography is the scientific study of the oceans, which cover more than 71 percent of Earth's surface. It is divided into four major areas of research: physical, chemical, biological, and geological.

Physical oceanography is the study of basic activities of the oceans such as currents, tides, boundaries, and even evaporation. Chemical oceanography is the study of the chemical parts of the sea and the presence and concentration of chemical elements such as zinc, copper, and nitrogen in the water. These two fields are the main focus of oceanography today. Current areas of research include oceanic circulationespecially ocean currents and their role in weather-related eventsand changes in sea level and climate. Also, as the population of the planet continues to increase, oceanographers have begun to conduct research on using the oceans' resources to produce food.

Biological oceanography is the study of all life in the sea, including plants, animals, and other living organisms. Since the oceans provide humans with vital food, biological oceanographers look for ways to increase these yields to meet growing populations.

Geological oceanography is the study of the geological structure and mineral content of the ocean floor. This includes mineral resource extraction (removal), seafloor mapping, and plate tectonics activities that offer clues to the origin of Earth. (Earth's crust is made up of large plates that fit together loosely. The study of these plates and their movement, especially their ability to cause earthquakes, is called plate tectonics.)

Ocean research vessels

The era of modern oceanography was opened with the four-year ocean exploration expedition of the H.M.S. Challenger, beginning in 1872. The Challenger was the first vessel used to systematically record information about all the oceans except the Arctic, including their depths, circulations, temperatures, and organic life.

Sophisticated sonar and magnetic technology on subsequent voyages by other vessels have greatly increased scientists' knowledge of the oceans, helping them make such important geological discoveries as

seafloor spreading (by which new oceanic crust is created) and plate tectonics. All ocean research ships are essentially floating laboratories. Many are operated and financed by the U.S. Navy, often in conjunction with a university or other institution.

Oceanographers of the twenty-first century use satellites to study changes in salt levels, temperature, currents, biological events, and transportation of sediments. As scientists develop new technologies, new doors will open on the study of the world's oceans.

[See also Ocean ]

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oceanography

o·cea·nog·ra·phy / ˌōshəˈnägrəfē/ • n. the branch of science that deals with the physical and biological properties and phenomena of the sea. DERIVATIVES: o·cea·nog·ra·pher / -fər/ n. o·cea·no·graph·ic / -nəˈgrafik/ adj. o·cea·no·graph·i·cal / -nəˈgrafəkəl/ adj.

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oceanography

oceanography Study of the oceans. The major sub-disciplines of oceanography include marine geology (see plate tectonics), marine biology, marine meteorology, and physical and chemical oceanography. The science of oceanography dates from the Challenger expedition (1872–76). Jacques Cousteau's invention of the scuba aided human exploration of the seas. In 1948, August Piccard invented the bathyscaphe to explore deep waters.

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oceanography

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